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问题 选择题

如果等腰三角形的两边长分别是方程x2-10x+21=0的两根，那么它的周长为（　　）

A．10

B．13

C．17

D．21

答案

∵x2-10x+21=0，

∴（x-3）（x-7）=0，

∴x1=3，x2=7，

当等腰三角形的边长是3、3、7时，3+3＜7，不符合三角形的三边关系，应舍去；

当等腰三角形的边长是7、7、3时，这个三角形的周长是7+7+3=17．

故选C．

单项选择题 B1型题

容易引起Ⅱ型呼吸衰竭加重的药物是（）

A.呼吸兴奋剂

B.袢利尿剂

C.强心剂

D.镇静剂

E.血管扩张剂
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单项选择题

Are you a man or a mouse When people ask this question they want to know (1) you think you are a (2) person or a coward. But you will never really know the answer to this question (3) you are tested in real life. Some people (4) they are brave but when they come face to face with real (5) , they act like cowards. Others think of themselves as cowards, but when they meet danger, they act like (6) .Lenny had always thought of himself as a (7) person. He got worried before examinations. He worried about his job and health. All he wanted in life was to be safe and healthy. (8) , on January 15th, 2002, a plane crashed into the Potomac River in Washington. Lenny went to the river to See what was happening. He saw a woman in the (9) water. Lenny did not feel afraid. He kept very (10) and did a very dangerous thing. He jumped into the Potomac, (11) to the woman, and kept her head (12) the water. Seventy-eight people died that day. Thanks to Lenny, it was not (13) .When you are in a very (14) situation and feel afraid, the body automatically produces a chemical in the blood. The chemical is called adrenalin. (15) adrenalin in the blood system, you actually feel per and per and are (16) to fight or run away. However, when you are absolutely terrified, the body can produce too much adrenalin. Where this (17) , the muscles become very hard and you find you (18) move at all. You are then paralyzed with fear. This is (19) when we are very frightened, we sometimes say we’re "petrified". This word comes from the Greek word "petros", which means "stone". We are (20) frightened that we become stonelike.

第（4）空应选择（）

A．realize

B．find

C．think

D．agree
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